Entrance to Cobalt Scar must initially be gained by traveling through Skyshrine. A Shrine Key is required to use the teleporter from the dragon city to the tower here or have someone group with you and use the one they have to click you through. Once you obtain the key(tooth) from the dragon portal, however, you can also teleport here. Key quest can be found here
https://wiki.project1999.com/Key_to_Cobalt_Scar